During the crimping process of a workpiece the increasing plastical deformation of the workpiece between the dies requires a crimping force which increases during the crimping process. For known crimping pliers the hand forces manually applied upon hand levers of the crimping pliers are transmitted to the dies by a drive mechanism such that it is possible to generate the required maximal crimping forces by manual actuation of the hand levers.
The publications DE 197 13 580 C2, DE 197 09 639 A1, DE 199 24 086 C2, DE 199 24 087 C2, DE 199 63 097 C1, DE 103 46 241 B3, DE 10 2007 001 235 B4, DE 10 2008 007 303 B4 disclose embodiments of crimping pliers wherein the drive mechanism is built with a toggle lever drive. Here, the crimping pliers are built with a C-shaped pliers head in which crimping jaws are moved with a translational movement towards each other by the toggle lever drive. It is also possible that the pliers head has a “scissors-like” design with crimping jaws being pivot-mounted at each other. Here, a toggle lever of the toggle lever drive is linked to one of the crimping jaws. During the working stroke from an open position into a closed position of the crimping pliers the toggle lever angle built between the toggle levers in the region of the toggle lever joint changes. When approaching the closed position, the toggle lever angle approximates an angle of 180°. This kinematic of the toggle lever drive has the consequence that at the beginning of the working strokes small crimping forces are produced with a comparatively large closing movement of the pliers jaws during a part of the stroke of the hand levers, and at the end of the working stroke large crimping forces are produced with a small closing movement of the pliers jaws in the corresponding part of the stroke of the hand levers. Here, the chosen lengths of the toggle levers and the linking points of the toggle levers at the hand levers and pliers jaws and accordingly the angular setting determine the characteristic of the closing movement of the pliers jaws and the produced crimping forces dependent on the closing movement of the hand levers.
The publication of the design U.S. 341,303 discloses crimping pliers for crimping fittings for tube connections. For these crimping pliers it is possible to pivot the pliers jaws about a common rotational joint. A pliers jaw is rigidly connected with a fixed hand lever, whereas the other pliers jaw is coupled by a pivoting joint with a movable hand lever. Here, a toggle lever drive is built according to the principle “roller-curve” as follows: A roller is mounted for pivoting about a roller axis at the fixed hand lever. The movable hand lever carries a guiding part which forms a curved track. For a movement of the hand levers towards each other the movable hand lever is supported with the curved track at the roller which is pivot-mounted at the fixed hand lever. In this case, one toggle lever is built by the roller, namely the material region of the roller extending between the contact point of the roller at the curved track and the roller axis. Instead, the other toggle lever is built between the contact point between the roller and the curved track and the pivot axis at which the movable hand lever is linked to the movable pliers jaw. The “toggle lever joint” is for this embodiment built by the rolling contact of the roller with the curved track so that there is no “joint” in the classical sense. If during the closing movement of the hand levers the roller rolls along the curved track, dependent on the contact point of the roller with the curved track the length of the last mentioned toggle lever changes and the position of the toggle lever joint at the curved track changes. Accordingly, by the choice of the geometry of the curved track, it is possible to additionally affect the characteristic of the crimping pliers.
For crimping pliers so-called forced locking units are used which serve for the following purposes:
a) By use of a forced locking unit it is intended to provide that it is only possible to open the hand levers and accordingly to open the crimping pliers when having completely run through the whole working stroke of the crimping pliers so that the crimping process has completely been terminated.
b) It is possible that during travel through the working stroke after a part of the stroke the actuating forces applied by the user to the hand levers are reduced. This might e.g. be the case for an interruption of the crimping process or if the user intends to change the gripping of the crimping pliers so that the user changes his grip. If there was a reduction of the crimping force, this might result in a dislocation of the workpiece relative to the die which is undesired. Once a partial crimping step is reached, by use of the forced locking unit it is possible to secure the reached partial crimping step so that also for a reduction or removal of actuating forces applied upon the hand levers the crimping jaws are not able to perform an opening movement or are only able to perform an opening movement of reduced extent.
Crimping pliers having a forced locking unit are e.g. known from DE 20 2012 102 561 U1, DE 10 2013 100 891 A1, DE 299 14 764 U1 and EP 1 820 607 A2.
DE 10 2007 056 262 A1 discloses crimping pliers wherein a toggle lever drive is built according to the above explained principle roller-curve. In these crimping pliers a forced locking unit is used. Here, a toothing of the forced locking unit is located at the end region of the movable pliers jaw facing away from the die, whereas a spring-biased latching pawl of the forced locking unit is pivot-mounted to the movable hand lever.
For the formation of the drive mechanism with a toggle lever drive without use of the principle roller-curve, usually a toothing of a forced locking unit is built by a protrusion of a toggle lever which is also denoted as a pressure lever. This toothing cooperates with a latching pawl which is pivot-mounted to the movable hand lever under the bias of a spring (cp. EP 0 732 779 B1).